The MetPak RG weather station is supplied with digital SDI-12, RS232 & 422 outputs.
Low power consumption enables this weather station instrument to be used
in remote locations where power is at a premium. An electrical junction box is fitted
to the mounting bracket allowing convenient termination of all electrical cables.

MetPak Pro Base Station

MetPak Pro is available as a Base Station which enables the system to be
specified with a remote wind sensor if required. This sensor can be
positioned away from the Base Station and a connection cable is provided.

The Base Station has been tested in accordance with BSEN 60945 and is
suitable for use in marine environments. This system, which includes inputs
for a Pt100 temperature sensor, tipping bucket rain gauge and two analogue
sensors, can also be specified without a wind sensor if wind measurement
data is not required.

The MetPak Pro base station can be specified with a remote sensor from
any of the options below:

An optional heater interface box is available for ease of connection for
remote heated wind sensors.

An optional MetPak Pro junction box allows an alternative method to
connect the sensors to the base station in a convenient separate box.

MetPak Pro with Integrated WindSonic

This variant of the MetPak Pro features the same on-board sensors as the
Base Station, with an integrated WindSonic ultrasonic wind sensor for high
accuracy wind speed and direction measurement. This unit also features
inputs for up to four external measurement devices including the precision
tipping bucket Rain Gauge.

» No moving parts - no bearings to wear or require replacement
» Very low start up speed
» 0 to 360° operation - no dead band
» Single robust sensor
» Designed to withstand a 1m drop test
» No calibration
» Low cost of ownership
» 2 year warranty

Configuring the MetPak

To change the setting of a MetPak weather station from the default
factory settings, it is possible to communicate with the instrument direct
from a PC.

MetPak can be configured using:

» A terminal program such as MS Windows HyperTerminal
» MetSet Configuration Software: MetSet is a free software package
that allows the user to configure the output and display data provided
by the MetPak II. The simple interface features a range of drop-down
selection boxes, providing the ability to enable or disable existing
sensors and adjust output rates.

MetView software is also provided free with each weather station, offering a clear, intuitive display of the current weather conditions.

MetView features five gauges: Temperature, Humidity, Pressure, Wind Speed and Wind direction. There is also a digital readout of Dew Point.

How Ultrasonic Wind Sensors Work

The WindSonic sensor uses the time of flight method of air velocity measurement.

There are four ultrasonic transducers arranged as two pairs at right
angles to each other. Each pair is used to measure the component of the wind
in the direction between the transducers.

For example if one pair is on a North South line and the other pair is on
an East West line then the North South component VN
and the East West component VE are measured. These are then combined to give the actual wind speed and direction.

Wind angle A = arctan ( VE / VN )

Wind speed S = sqroot ( VE2 + VN2 )

To look at how the component measurements are done we will take the example of the North South transducer pair:

A pulse of ultrasonic sound is transmitted by the North transducer and
the time T1 it takes to travel to the South transducer is accurately measured. The time
T2 is then measured for an ultrasonic pulse to
travel in the opposite direction from the South transducer to the North
transducer. These times are affected by the wind blowing along the line
between the transducers. For example if there is some wind blowing from a
Northerly direction, then the time taken for the ultrasonic pulse to travel
from N to S will be shorter than from S to N.

The time for the pulse to travel from N to S is given by

T1 = L / ( C + VN )

and the time for the pulse to travel from N to S is given by

T2 = L / ( C - VN )

whereL is the distance between the transducers andC the speed of sound